1. Field of the Invention
This invention relates to a method for the manufacture of a honeycomb catalyst. More particularly, the invention relates to a method for the manufacture of a ceramic honeycomb catalyst of monolithic construction capable of enhanced resistance to thermal shocks.
2. Description of Prior Arts
Generally a honeycomb catalyst is a composite formed by depositing on a ceramic carrier of monolithic construction a catalyst composition formed preponderantly of an active refractory metal oxide such as alumina, alumina-silica, titania or zirconia and a catalyst component made of a platinum family metal such as platinum, palladium, rhodium or ruthenium, and further incorporating, when necessary, a transient metal such as copper, nickel, cobalt or iron, or an oxide thereof, and a rare earth element such as cerium or lanthanum.
This honeycomb catalyst is extensively used in internal combustion engines such as of automobiles for treating their exhaust gases and depriving them of air pollutants such as carbon monoxide, hydrocarbons and nitrogen oxides, and in industries in general for deodorizing waste gases and encouraging catalytic combustions aimed at primary energy generation. When it is used for an automobile, for example, since the temperature of the catalyst in use is varied minute by minute by the operating condition of the automobile, the honeycomb catalyst is required to possess an ability to resist thermal shocks. In the honeycomb catalyst of monolithic construction, strain tends to develop between the ceramic honeycomb carrier and the catalyst composition deposited on the carrier because they have different thermal expansion coefficients. As the cycle of violent temperature change often repeats, the honeycomb catalyst eventually sustains cracks. When the cracks gradually gain in growth, they may break the catalyst itself into two or more pieces and jeopardize safe service of the catalyst in the worst case. The possibility of the honeycomb catalyst encountering this accident has been pointed out.
Particularly when the honeycomb catalyst is disposed near the engine outlet, because the exhaust gas has a high temperature and the working temperature of the honeycomb catalyst is accordingly fluctuated in a wide renge, it naturally follows that the honeycomb catalyst is demanded to possess high physical strengths, particularly high resistance to thermal shocks.
When the honeycomb catalyst is used in an ordinary industry such as for the purpose of burning a fuel on the honeycomb catalyst thereby ensuring complete-oxidation combustion of the fuel and utilizing the heat of the combustion as the primary energy source for a gas turbine, for example, the honeycomb catalyst is destined to undergo a sharp rise of temperature at the outset of the operation and a sharp fall of temperature at the termination of the operation.
If the thermal shocks due to the sharp temperature changes break the catalyst, there ensues a possibility that some of the fragments of the broken catalyst will injure the turbine or cause other similar serious accidents. In this application, therefore, the honeycomb catalyst is likewise demanded to possess an ability to resist thermal shocks.
An object of this invention, therefore, is to provide a novel method for the manufacture of a honeycomb catalyst.
Another object of this invention is to provide a method for the manufacture of a ceramic honeycomb catalyst of monolithic construction capable of enhanced resistance to thermal shocks.